Process

ABSTRACT

The present invention relates to a continuous hydroformylation process for the production of an aldehyde by hydroformylation of an olefin which comprises: providing a hydroformylation zone containing a charge of a liquid reaction medium having dissolved therein a rhodium hydroformylation catalyst comprising rhodium in combination with carbon monoxide and a ligand; supplying the olefin to the hydroformylation zone; maintaining temperature and pressure conditions in the hydroformylation zone conducive to hydroformylation of the olefin; recovering from the liquid hydroformylation medium a hydroformylation product comprising aldehyde; recovering from the hydroformylation zone a stream comprising the rhodium catalyst; contacting at least a portion of the stream with a solid acidic absorbent under process conditions which allow at least some of the rhodium to become bound to the absorbent; subjecting the rhodium bound to the absorbent, under process conditions which allow desorption of the metal, to a fluid stripping medium comprising hydrogen and solvent; recovering the rhodium hydride catalyst; and recycling the rhodium hydride catalyst to the hydroformylation zone.

[0001] The present invention relates to an improved hydroformylationprocess. In particular, it relates to a process for the hydroformylationof olefins to give aldehydes. Most particularly, it relates to a processfor the hydroformylation of C₂ to C₂₀ olefins or higher in which processconditions may be used which have not been possible heretofore.

[0002] Hydroformylation is a well known reaction in which an olefin,usually a terminal olefin, is reacted under suitable temperature andpressure conditions with hydrogen and carbon monoxide in the presence ofa hydroformylation catalyst to give an aldehyde, or a mixture ofaldehydes, having one more carbon atom than the starting olefin. Thus ahydroformylation reaction with propylene will yield a mixture of n- andiso-butyraldehydes, of which the straight chain n-isomer is usually themore commercially desirable material. The hydrogen and carbon monoxidewill generally be supplied to the hydroformylation reactor as synthesisgas.

[0003] Examples of hydroformylation processes can be found in U.S. Pat.No. 4,482,749, U.S. Pat. No. 4,496,768 and U.S. Pat. No. 4,496,769 whichare incorporated herein by reference.

[0004] The catalysts first used in hydroformylation reactions werecobalt-containing catalysts, such as cobalt octacarbonyl. However, thepresence of these catalysts meant that the reactor had to be operated atexceptionally high pressures, e.g. several hundred bars, in order tomaintain the catalysts in their active form.

[0005] Rhodium complex catalysts are now conventionally used in thehydroformylation of both internal olefins and alpha-olefins, that is tosay compounds containing the group —CH═CH₂, —CH═CH—, >C═C<, >C═CH—,—CH═C< or >C═C₂H. One advantage of these catalysts is that loweroperating pressures, e.g. to about 20 kg/cm² absolute (19.6 bar) orless, may be used than was usable with the cobalt catalysts. A furtheradvantage noted for the rhodium catalysts was that they are capable ofyielding high n-/iso-aldehyde product ratios from alpha-olefins; in manycases n-/iso-aldehyde molar ratios of 10:1 and higher can be achieved.

[0006] Further, since the rhodium catalyst is non-volatile, productrecovery was greatly simplified. A fuller description of the process canbe found in the article “Low-pressure OXO process yields a betterproduct mix”, Chemical Engineering, Dec. 5, 1977. Also relevant to thisprocess are U.S. Pat. No. 3,527,809, GB-A-1338237 and GB-A-1582010 whichare incorporated herein by reference.

[0007] The rhodium catalyst generally adopted in commercial practicecomprises rhodium in complex combination with carbon monoxide and withan organo-phosphorous ligand, for example triphenylphosphine. Althoughthe nature of the catalytic species is not entirely clear, it has beenpostulated that where the ligand is triphenylphosphine it isHRh(CO)(PPh₃)₃ (see, for example, page 792 of “Advanced InorganicChemistry” (Third Edition) by F. Albert Cotton and Geoffrey Wilkinson,published by Interscience Publishers).

[0008] The reaction solution for the hydroformylation reaction willgenerally contain excess ligand.

[0009] U.S. Pat. No. 3,527,809, which is incorporated herein byreference, proposes the use of other ligands, including phosphites, suchas triphenylphosphite.

[0010] Whilst the use of rhodium catalysts offers various advantages, itdoes suffer from the disadvantage that it is very expensive. It istherefore desirable to utilise this highly expensive metal in the mosteconomically effective way.

[0011] During operation of the reactor, the catalyst may becomedeactivated and therefore needs to be removed from the reactor such thatfresh active catalyst can be added. The removed catalyst will generallybe processed to recover the metal values.

[0012] The deactivated catalyst may have been thermally deactivated,i.e. clustered and/or chemically deactivated, i.e. poisoned orinhibited.

[0013] In some cases although the catalyst may be chemically active, thecatalyst solution includes such a high concentration of non-volatilematerial that it is of no further practical use.

[0014] Although the mechanism of deactivation in aryl phosphine ligandedsystems by the formation of clusters is not entirely clear, it isbelieved that rhodium clusters, having phosphido bridges may be formed,for example, by the loss of one or more phenyl groups from the arylphosphine molecule. The formation of clusters is generally increased asthe temperature is increased.

[0015] The chemical deactivation may be poisoning such as by sulphurcompounds, chloride, cyanide and the like.

[0016] The chemical deactivation may also be inhibition of the catalyst.Inhibitors that may be found in, for example, propylene and butylenehydroformylation include acetylenes and acroleins.

[0017] Since the rhodium catalyst is generally used in low concentrationbecause of its high cost and activity, the effect of any poisons orinhibitors present is high. It is therefore usually necessary to reducethe presence of these poisons and inhibitors present in the feed to verylow levels.

[0018] Rhodium catalysed hydroformylation processes can be classifiedinto two main categories, namely those in which the aldehyde product isremoved by liquid/liquid separation processes and those in which theproduct is removed by a vapour path process.

[0019] In the processes in which the aldehyde product is removed by aliquid/liquid separation process, the aldehyde product is obtained asone liquid phase while the ligand and rhodium/ligand complex remains inanother phase and is returned to the reaction zone. This type of processhas the advantage of being independent of the volatility of the aldehydeproduct and the volatility of the relatively less volatile aldehydecondensation by-products. These processes do, however, have their owndisadvantages including interphase solubility/entrainment problems inwhich some of the rhodium may leave in the aldehyde product-containingphase, low selectivity to the desired aldehyde isomer and low reactionrate as a consequence of the low solubility of the reactants in anaqueous base reaction medium.

[0020] Where the aldehyde product is recovered from the catalyst by avapour path process this has conventionally been effected in one of twoways.

[0021] Where lower olefin feedstocks are used, a stream of synthesis gasand olefin is passed through the reactor solution, condensed and afterseparation of the liquid condensate the gas phase is returned to thereactor via a compressor. Suitable means is used to prevent the rhodiumsolution leaving the reactor by liquid droplet entrainment in the gasphase these include restricting the superficial velocity of the gasthrough the reactor to less than a specific value and passing thegas/vapour stream through a liquid droplet de-entrainment device beforeexiting the reactor. Addition of make-up streams of synthesis gas andolefin are required to maintain the system pressure and reaction rate asthe reactants are consumed. A purge stream of gas after the condensationstage is generally required to remove any inert gases accumulating inthe system and also to control the level of paraffins that either enterthe system with the olefin feed or are produced by olefin hydrogenationin the reactor. This type of process is generally known as a Gas RecycleProcess.

[0022] An important feature of the Gas Recycle Process is that toachieve stable reactor conditions, every product of the reaction mustleave the reaction system at it's rate of formation, thus the relativelyless volatile materials (such as aldehyde condensation products)accumulate in the reactor solution to a relatively high concentrationuntil the rate of removal of products in the vapour phase equals theproduction rate of each material. This can be achieved for long periodswhen the feed olefin is ethylene or propylene but even with propylenethere can be a slow accumulation of aldehyde condensation tetramers andpentamers such that the reactor solution volume will slowly increasewith time.

[0023] If progressively higher olefins such as butenes, pentenes,hexenes etc. are supplied to a gas recycle system the requirement for ahigher gas recycle rate means that the gas superficial velocity limit isexceeded unless a reactor solution volume that is increasingly wide andshallow is used as the olefin molecular weight increases. Thus, whilstthis arrangement goes some way towards addressing the problems detailedabove, the arrangement suffers from new problems associated withgas/liquid mass transfer and reactor mechanical/economic design issues.

[0024] In an alternative solution to the problem associated with the useof higher olefins, the temperature of the reaction system is increasedsuch that every component becomes more volatile. Again, whilst thisarrangement goes some way to solving the above problem, fresh problemsare noted. In this case, increased production of heavy aldehyde selfcondensation by-products and increased catalyst deactivation byincreased clustering rates occurs.

[0025] These considerations mean that the Gas Recycle Process is limitedto the hydroformylation of ethylene and propylene with thehydroformylation of butenes and pentenes being marginal and verymarginal cases respectively.

[0026] These considerations led to the development of the so called“Liquid Recycle Process”. In this process a volume of solution iscontinuously withdrawn from the hydroformylation reaction zone or zonessuch that the liquid level in the or each zone is held constant. Thiswithdrawn liquid is then subjected to a single or multistage evaporationoperation where the temperature, pressure and residence times areselected to recover the products and by-products as well as to protectthe catalyst activity. The concentrated catalyst solution is thenreturned to the hydroformylation reaction zone. Olefin and synthesis gasare supplied to the or each hydroformylation reaction zone to maintainthe desired reaction rate and conditions.

[0027] The liquid recycle process has been shown to provide benefitseven for the hydroformylation of propylene where higher volumetricproductivity and lower operating costs can be achieved, and is essentialfor the economic production of C₅ and higher aldehydes.

[0028] As olefins of increasing molecular weight are hydroformylated bythe Liquid Recycle Process the removal of the heavy by-products byevaporation requires lower and lower pressures and/or higher evaporationtemperatures. Thus, despite the advantages noted for this process,eventually the accumulation of heavy by-products in the reactor solutionoccurs such that the reactor volume increases uncontrollably. Thisdisadvantage of the system is referred to as “heavies drowning”. Whereheavies drowning occurs, there has to be a purge of catalyst solution(containing ligand and active catalyst) to control this accumulation.

[0029] It has been suggested, for example in U.S. Pat. No. 5,053,551,that the addition of inert diluents can delay heavies accumulation todefer the heavies drowning effect and confer a longer useful catalystlife. Whilst the system goes some way to addressing the problem, itcannot prevent eventual heavies drowning from occurring.

[0030] Thus during the operation of a liquid recycle hydroformylationplant the reaction and product recovery conditions are in a state ofcontinuous change due to the changes in solution composition andcatalytic activity. The accumulation of essentially non volatilealdehyde condensation products requires that the pressure and/ortemperature of the product evaporator needs progressive adjustment. Theaccumulation of inhibitors and poisons in the reactor solution alsorequires the progressive adjustment of reaction conditions to maintainthe conversion and selectivity of the system. High temperatureevaporation and poisons in the olefin feed can also result in the lossof catalytically active rhodium by poisoning and/or the formation ofrhodium clusters requiring the continuous or periodic removal of a partof the catalyst recycle stream and its replacement by fresh catalyst andligand.

[0031] Thus, it will be understood that whichever hydroformylationmethod is selected, the economic need to run the plant for maximumproduction of product must be balanced with the need to conserve thelife of the expensive catalyst. It is therefore desirable to adoptcatalyst management systems which maximise productivity whilstminimising the damage to the catalyst.

[0032] One catalyst management system which may be adopted comprisescharging a first charge of catalyst to the plant. As the productivity ofthe plant begins to decline it is necessary to adapt the utilities andseparation units of the plant to the reduced flow of aldehyde and thereduced consumption of synthesis gas. Care is taken to ensure that thetemperature does not increase since any such increase will result in anaccelerated decline in the catalyst activity and increased formation ofthe heavies. When product flow falls to a level that is unacceptable,the plant operator may choose to raise the temperature with theattendant problems or add additional catalyst.

[0033] Although increasing temperature does have the drawbacks detailedabove it does not incur the capital expenditure of catalyst purchase andmay therefore be the preferred initial approach. Any step change in thetemperature will require a corresponding step change in the operation ofthe utilities and separation units.

[0034] After any increase in temperature the productivity will continueto decline but at an increased rate. Further increases in temperaturemay be carried out until a decision is made that any further increasewill result in an unacceptable rate of catalyst deactivation. At thispoint further catalyst may be added to the reactor. However, increasingthe catalyst concentration will also increase the rate of thermaldeactivation and the consequential loss of activity. Thus there is anupper practical limit on the amount of rhodium which may be added to thereactor. Eventually it will be necessary to shut down the plant.

[0035] One alternative catalyst management system involves taking acontinuous purge of the reactor solution which can then be reprocessedto recover the catalyst and remove the heavies. In practice, economicsrequire that the catalyst be reprocessed in large batches and results insignificant loss of rhodium metal. This results in high capitalexpenditure for the plant owners.

[0036] Where triphenylphosphine is used as ligand, it may react with theolefin to produce the corresponding alkyldiphenylphosphine. Since thealkyldiphenylphosphines are stronger complexing agents than thetriphenylphosphine, a catalyst solution of lower activity andselectivity to the linear product is obtained.

[0037] These mechanisms of catalyst degradation become progressivelymore onerous as the molecular weight of the olefin increases, requiringprogressively higher catalyst purge rates.

[0038] Conventionally, the operators of the gas or liquid recycle planthave had to collect the active and/or inactive catalyst by shutting downthe reactor, removing some or all of the catalyst solution andconcentrating it to partially separate it from the other componentspresent. Additionally, or alternatively, partially deactivated orheavies drowned catalyst may be continuously collected from reactorstreams. By reactor stream we mean any stream which is obtained from anypoint in a process and which will contain rhodium metal catalyst. In thecase of the liquid recycle process, the stream will usually be thecatalyst recycle stream after evaporation of the hydroformylationproducts.

[0039] The conventional liquid recycle process must therefore besubjected to a continuous or episodic regime of adjustment in processconditions throughout the operating period and this is particularlymarked when the higher molecular weight olefins are used as feedstock.

[0040] Since the rhodium is generally only present at low concentration,it can be particularly difficult and costly to recover the rhodium fromthe very dilute solutions.

[0041] The rhodium organic solution has conventionally been concentratedby a variety of means before being shipped off-site for recovery. Thismeans that if the operation of the plant is not to be shut down for aprolonged period, the operator must purchase more of the very expensivecatalyst to operate the plant than he actually requires at any one time.

[0042] There are also environmental issues associated with the recoveryof the catalyst where phosphorous ligands are present.

[0043] A variety of means of recovering the rhodium from solution hasbeen suggested including precipitation followed by extraction orfiltration and extraction from the organic mixtures using, for example,amine solutions, acetic acid, or organophosphines.

[0044] Ion-exchange methods have also been suggested, for example inU.S. Pat. No. 3,755,393 which describes passing a hydroformylationmixture through a basic ion-exchange resin to recover rhodium. A similarprocess is described in U.S. Pat. No. 4,388,279 in which Group VIIImetals are recovered from organic solution using either a solidabsorbent such as calcium sulfate, an anionic ion-exchange resin ormolecular sieves.

[0045] An alternative arrangement is described in U.S. Pat. No.5,208,194 in which a process is described for removing Group VIII metalsfrom organic solutions which comprises contacting the organic solutionwith an acidic ion-exchange resin containing sulfonic acid groups. Thetreated solution is then separated from the ion-exchange resin and themetal values are recovered from the resin by any suitable means. Onemeans that is suggested is that the resin should be burnt off in anashing process which leaves the metal in a form suitable for recovery.

[0046] These prior art processes, whilst being suitable for separatingthe metal from the stream in which it was removed from the reaction,suffer from the disadvantage that the operator of the reactor must sendthe recovered metal concentrate off-site to be converted into an activeform. Further, where the stream removed from the reactor includes activecatalyst, the separation procedure will either leave it in a form inwhich it cannot be returned to the reactor or will cause it to bedeactivated such that it is no longer suitable for use in the reactorand removal off-site for regeneration is required.

[0047] In U.S. Pat. No. 5,773,665, a process is suggested which enablesactive catalyst contained in a stream removed from a hydroformylationprocess to be separated from the inactive catalyst and the activecatalyst following treatment, to be returned to the hydroformylationreactor. In the process a portion of the recycle stream from thehydroformylation reaction is passed through an ion exchange resin columnto remove impurities and active rhodium and the thus purified recycledstream, which may contain inactive catalyst, is returned to thehydroformylation reactor.

[0048] The impurities, which may include aryl phosphine oxide, alkylphosphine oxide, mixed phosphine oxide and high molecular weight organiccompounds, are removed from the resin by washing with, for example, anorganic solvent. The effluent from this wash is removed as a wastestream. The active catalyst remains bound to the resin during thiswashing process.

[0049] The resin is then treated with a catalyst removal solvent such asisopropanol/HCl to produce a stream containing “active” rhodium catalystfor eventual recycling to the hydroformylation reactor. Whilst thecatalyst has not been deactivated by thermal or chemical means and istherefore referred to as “active” it is not in a form in which it willactually act as a catalyst in the reactor. Thus, before the catalyst canbe recycled it must first be removed from the resin using a strong acidreagent and then converted to the hydridocarbonyl by treatment withhydrogen and carbon monoxide in the presence of an acid scavenger and aligand to make it a truly active catalyst.

[0050] In an optional arrangement, the inactive rhodium catalyst, i.e.the clustered catalyst, which passed through the ion-exchange resinwithout being absorbed and which is contained in the purified recyclestream may be reactivated by conventional technology such as by wipedfilm evaporation followed by oxidation and subsequent reduction beforebeing returned to the reactor. Thus this inactive catalyst is nottreated by the ion-exchange resin.

[0051] Whilst this process goes some way to improving the conventionalhydroformylation process by recycling some of the rhodium, in that itsuggests a means of separating the active catalyst on site, it suffersfrom various disadvantages and drawbacks in particular thosedisadvantages associated with the need to treat the “active” catalystafter it has been removed from the ion-exchange resin and before it canbe returned to the reactor. Indeed it is the ion-exchange treatmentwhich means that the catalyst is no longer suitable for use in thereactor. Although in a preferred embodiment, U.S. Pat. No. 5,773,665does suggest that the thermally deactivated catalyst may be regeneratedbefore return to the reactor, the overall plant described therein isexpensive to construct and operate because of the number of separationand treatment steps required to achieve full recycle. The problem isparticularly exacerbated as some of the steps are carried out in thepresence of corrosive acid media A further drawback associated with thepresence of acid media is the costs associated with the consumption ofbase required to neutralise the acid.

[0052] There is therefore a desire to produce a process for theproduction, on a continuous basis, of aldehydes from olefins byhydroformylation using a liquid recycle process under constantconditions chosen by the plant operator for extended, preferablyindefinite, periods of time whilst providing maximum utilisation of thecatalytic metal and ligand.

[0053] Thus according to the present invention there is provided acontinuous hydroformylation process for the production of an aldehyde byhydroformylation of an olefin which comprises:

[0054] (a) providing a hydroformylation zone containing a charge of aliquid reaction medium having dissolved therein a rhodiumhydroformylation catalyst comprising rhodium in combination with carbonmonoxide and a ligand;

[0055] (b) supplying the olefin to the hydroformylation zone;

[0056] (c) maintaining temperature and pressure conditions in thehydroformylation zone conducive to hydroformylation of the olefin;

[0057] (d) recovering from the liquid hydroformylation medium ahydroformylation product comprising aldehyde;

[0058] (e) recovering from the hydroformylation zone a stream comprisingthe rhodium catalyst;

[0059] (f) contacting at least a portion of the stream with a solidacidic absorbent under process conditions which allow at least some ofthe rhodium to become bound to the absorbent;

[0060] (g) subjecting the rhodium bound to the absorbent, under processconditions which allow desorption of the metal, to a fluid strippingmedium comprising hydrogen and solvent;

[0061] (h) recovering the rhodium hydride catalyst; and

[0062] (i) recycling the rhodium hydride catalyst to thehydroformylation zone

[0063] In a most preferred arrangement, the stream from step (e) isdivided and a first part is recycled to the hydroformylation zone andthe second part is subjected to steps (f) to (i). Any suitable amount ofdivided stream may be passed to steps (f) to (i). However, thesubstantial benefits of the present invention are achievable even ifsmall amounts, such as amounts of the order of 1% or even less such asamounts of the order of 0.01%, are subjected to steps (f) to (i).

[0064] It will be understood that the recycled rhodium hydride catalystfrom step (i) will be utilised in the further hydroformylation reaction.

[0065] The stream recovered from the hydroformylation zone in step (e)may be any stream which is obtained from any point in thehydroformylation process and which will contain rhodium metal catalyst.In the case of the liquid recycle process, the stream will usually bethe catalyst recycle stream after evaporation of the hydroformylationproducts.

[0066] The arrangement of the present invention enables substantialbenefits to be obtained. First, the recovery and recycling of thepresent invention enables the plant operator to run the plant with lesscatalyst than has been required heretofore. This is because it is notnecessary to hold catalyst in stock to replace catalyst which is shippedoff-site for recovery and regeneration.

[0067] The catalyst recovery arrangement of steps (f) to (i) areparticularly efficient in separating catalyst from heavies and thereforethe system allows for the heavies formation in the reactor or elsewherein the system to be readily managed without having a deleterious effecton the operation of the reactor. This is because the process of thepresent invention is particularly suitable for removing the rhodiumhydride catalyst from reactor streams containing molecules having a highmolecular weight and hence low volatility and which are thereforedifficult to separate from the catalyst by conventional means.

[0068] Examples of these heavies, which are generally high boilingby-products, include organic condensation products and will includecyclic trimers and higher cyclic moieties and linear and branchedpolymeric moieties which could also be present in the feed to thereactor.

[0069] Further, the presence in the system of the catalyst recycleallows for control of the level of non-volatile inhibitors present inthe reactor system and may facilitate long term operation at constantreaction and vaporiser temperatures.

[0070] Since the catalyst can be readily recovered and/or heaviesreadily removed, by the process of the present invention, the plantoperator may choose to operate the plant at conditions which haveheretofore not been practicable because of catalyst deactivation and/orheavies formation. Thus, for example, higher temperatures in bothreactor and vaporiser may be usable which will enable an increased rateof production of the aldehyde.

[0071] Thus the present invention provides a hydroformylation process inwhich continuous recycling of the rhodium catalyst allows for theoverall productivity to be maintained constant despite on-goingdeactivation of the catalyst and heavies formation. As this allows forthe previously required step changes in productivity to be obviated, theease of operation and the efficiency of the reaction is enhanced. Theprocess may also allow feedstocks to be processed which could not beutilised for hydroformylation because of the presence of moieties whichwould poison and/or inhibit the catalyst or which had a high heaviesforming capability.

[0072] It will be understood, that these benefits can be obtained eitherby operating the rhodium recovery steps (f) to (i) continuously orperiodically.

[0073] The olefin used in the hydroformylation reaction of the presentinvention contains at least one olefinic carbon-carbon double bond.Preferably the olefin contains from 2 to about 20 carbon atoms althoughit will be understood that higher olefins may be used. Included withinthe term “olefin” are not only alpha-olefins, i.e. olefins containingthe group —CH═CH₂ or >C═CH₂ but also internal olefins containing thegroup —CH═CH—, —CR₁═CH—, or —CR₁═CR₁— where R is an organic moiety, aswell as compounds containing both alpha-olefinic and terminal olefinicgroups.

[0074] Illustrative olefins include olefinically unsaturatedhydrocarbons, e.g., alkenes, arylalkenes, and cycloalkenes, as well assubstituted olefins, e.g. ethers of unsaturated alcohols, and esters ofunsaturated alcohols and/or acids.

[0075] Examples of suitable olefins include alpha-olefins (e.g.ethylene, propylene, butene-1, iso-butylene, pentene-1,2-methylbutene-1, hexene-1, heptene-1, octene-1,2,4,4-trimethylpentene-1, 2-ethylhexene-1, nonene-1, 2-propylhexene-1,decene-1, undecene-1, dodecene-1, octadecene-1, eicosene-1,3-methylbutene-1, 3-methylpentene-1, 3-ethyl-4-methylpentene-1,3-ethylhexene-1,4, 4-dirnethylnonene-1, 6-propyldecene-1, 1,5-hexadiene,vinyl cyclohexane, allyl cyclohexane, styrene, alpha-methylstyrene,allylbenzene, divinylbenzene, 1,1-diphenylethylene, o-vinyl-p-xylene,p-vinylcumene, m-hexylstyrene, 1-allyl-4-vinylbenzene,beta-vinylnaphthalene, and the like), alpha-alkenols, (e.g. allylalcohol, hex-1-en-4-ol, oct-1-en-4-ol, and the like), alpha-alkenylethers (e.g. vinyl methyl ether, vinyl ethyl ether, allyl ethyl ether,allyl t-butyl ether, allyl phenyl ether, and the like), alpha-alkenylalkanoates (e.g. vinyl acetate, allyl acetate, and the like), alkylalpha-alkenoates (e.g. methyl acrylate, ethyl acrylate, n-propyloct-7-enoate, methyl methacrylate, and the like), alpha-olefinicallyunsaturated aldehydes and acetals (e.g. acrolein, acrolein dimethyl anddiethyl acetals, and the like), alpha-olefinically unsaturated nitriles(e.g. acrylonitrile, and the like), and alpha-olefinically unsaturatedketones (e.g. vinyl ethyl ketone, and the like). The term olefin alsoincludes internal olefins which contain preferably from 4 to about 20carbon atoms. Such compounds have the general formula:

R₁R₂C═CR₃R₄

[0076] in which R₁ and R₂ each represent a hydrogen atom or an organicradical or together represent a divalent radical which, together withthe indicated carbon atoms, form a carbocyclic or heterocyclic ring, andR₃ and R₄ each represent an organic radical or together represent adivalent radical which, together with the indicated carbon atoms, form acarbocyclic or heterocyclic ring.

[0077] As examples of internal olefins there may be mentioned cis- andtrans-butene-2, 2-methylbutene-2, 2,3-dimethylbutene-2,1,2-diphenylethylene, hexene-2, hexene-3, cis-and trans-heptane-2,decene-2, tetradecene-2, 4-amyldecene-2, 4-methyltridecene-2,octadecene-2, 6,6-dipropyldecene-3, prop-1-enylbenzene,3-benzylheptene-3, cyclobutene, cyclopentene, cyclohexene, cycloheptene,cyclooctene, 1-methylcyclohexene, diethyl maleate, diethyl fumarate,crotonaldehyde, crotonaldehyde dimethyl acetal, ethyl cinnamate, cis-and trans-prop-1-enyl t-butyl ether, and the like.

[0078] The hydroformylation reaction may be carried out on a mixture of2 or more olefins.

[0079] The or each olefin selected for the hydroformylation reactionwill be charged to the hydroformylation zone where it will be contactedwith hydrogen and carbon monoxide. One or more inert materials, such asinert gases (e.g. nitrogen, argon, carbon dioxide and gaseoushydrocarbons, such as methane, ethane, and propane) may also be present.Such inert gases may be present in the olefin feedstock, the synthesisgas or both. Other inert materials may include hydrogenation by-productsof the hydroformylation reaction, for example n-butane where the olefinis butene-1 or butene-2 and corresponding alkanes for other olefinstarting materials.

[0080] The process may be operated so that apart only of the olefin,e.g. from about 15% to about 80% or higher, is converted in passagethrough the hydroformylation zone. Although the process can be operatedon a “once through” basis, with unreacted olefin being exported,possibly for other uses, after product recovery, it may be desirable torecycle unreacted olefin to the hydroformylation zone.

[0081] As some isomerisation of olefin may occur in passage through thehydroformylation zone (for example in the case of butene-1 someisomerisation to butene-2 may occur) when using C₄ olefins or higher,the recycle olefin stream may in such cases contain a minor amount,typically about 10% or less, of isomerised olefin, even though theolefin feedstock is substantially free from other isomeric olefin(s). Inaddition it may contain by-product hydrogenated feedstock. Theconcentration of isomerised olefin(s) and of inert materials in therecycle stream or streams can be controlled in the conventional mannerby talking purge streams at appropriate controlled rates.

[0082] The feed of the olefin may be a mixed feedstock containing bothinternal and alpha-olefin components. For example, it is possible to usea mixed C₄ hydrocarbon feedstock containing, in addition to cis- andtrans-butene-2, also butene-1, iso-butylene, n-butane, iso-butane, andminor amounts of C₁₋₅ alkanes.

[0083] The olefin may be subjected to any suitable pretreatment beforebeing charged to the hydroformylation zone. However, the ability of theprocess of the present invention to readily remove heavies andregenerate catalyst means that pretreatment to remove impurities and thelike from the hydroformylation zone may not be required or may bereduced.

[0084] Thus, for example, in prior art arrangements, the presence of arhodium poison or inhibitor at a level of about 0.5 gram equivalent ofrhodium per cubic meter of feed, will result in complete deactivation ina period of the order of 200 days. With the present invention, thispresence in the feed of this level of poisons and/or inhibitors may bereadily accommodated.

[0085] The rhodium hydride catalyst used in the process of the presentinvention is preferably a rhodium carbonyl complex comprising rhodium incomplex combination with triphenylphosphine, triphenylphosphite or otherphosphorous ligands for example those described in U.S. Pat. No.4,482,749 which is incorporated herein by reference. Triphenylphosphineis particularly preferred.

[0086] The rhodium may be introduced into the reaction zone in anyconvenient manner. For example, the rhodium salt of an organic acid,such as rhodium acetate, i.e. [Rh(OCOCH₃)₂.H₂O]₂, can be combined withthe ligand in the liquid phase and then treated with a mixture of carbonmonoxide and hydrogen, prior to introduction of the olefin.

[0087] In one alternative arrangement the catalyst can be prepared froma carbon monoxide complex of rhodium, such as dirhodium octacarbonyl, byheating with the ligand which thereby replaces one or more of the carbonmonoxide molecules. It is also possible to start with the ligand ofchoice and finely divided rhodium metal, or with an oxide of rhodium(e.g. Rh₂O₃ or Rh₂O₃.H₂O) and the ligand, or with a rhodium salt of aninorganic acid, such as rhodium nitrate (i.e. Rh(NO₃)₃.2H₂O) and theligand, and to prepare the active species in situ during the course ofthe hydroformylation reaction.

[0088] In another alternative embodiment, it is possible to introduceinto the reaction zone, as a catalyst precursor, a rhodium complex suchas (pentane-2,4-dionato) dicarbonyl rhodium (I) which is then converted,under the hydroformylation conditions and in the presence of excessligand, to the operative species. Other suitable catalyst precursorsinclude Rh₄(CO)₁₂ and Rh₆(CO)₁₆.

[0089] The rhodium complex catalyst is preferably dissolved in theliquid reaction medium which comprises, in addition to the catalyticspecies, olefin, and a predetermined level of the phosphorous ligand.

[0090] Once the plant is operational the reaction medium may alsocomprise some or all of product aldehyde(s), aldehyde condensationproducts, isomerised olefin and hydrogenation product(s)derived from theolefin. The inert material detailed above may also be present. Thenature of the aldehyde condensation products, and possible mechanismsfor their formation during the course of the hydroformylation reaction,is explained in more detail in GB-A-1338237, which is incorporatedherein by reference.

[0091] Additionally the reaction medium may comprise a solvent, such asbenzene, toluene, acetone, methyl iso-butyl ketone, t-butanol,n-butanol, tetrain, decalin, ethyl benzoate and the like.

[0092] Usually, however, it will be preferred to operate in a “naturalprocess solvent”, i.e. a mixture of olefin or olefins, hydrogenationproduct(s) thereof, aldehyde product(s) and aldehyde condensationproducts. In addition, solvent from catalyst recovery may be present.However, when operating continuously or semi-continuously, it may bepreferred to use at start up a solvent, such as acetone, benzene,toluene, or the like, and then gradually to allow this to be displacedby “natural process solvent” by differential evaporation as the reactionprogresses.

[0093] The rhodium concentration in the liquid reaction medium may varyfrom about 10 ppm or less up to about 1000 ppm or more, calculated ineach case as rhodium metal and on a weight/volume basis. Typically therhodium concentration in the liquid reaction medium lies in the range offrom about 40 ppm up to about 200 ppm, calculated as rhodium metal. Foreconomic reasons it will not usually be desirable to exceed about 500ppm rhodium, calculated as metal, in the liquid reaction medium.

[0094] In the liquid reaction medium the ligand:Rh molar ratio is 1:1 orgreater but will be limited by solubility constraints.

[0095] Make-up ligand may be added and the addition may be continuous orintermittent. It may be added as the essentially pure compound or as asolution in a suitable solvent, e.g. one of the solvents previouslymentioned. If continuous addition is chosen then it can be added insolution form with the aid of a suitable dosing pump.

[0096] The hydroformylation conditions utilised in the process of thepresent invention involve use of elevated temperatures e.g. in the rangeof from about 40° C. to about 160° C. or more. Conventionally it will bepreferred to operate at as low a temperature as is possible i.e. fromabout 70° C. to about 95° C. as this will enable a satisfactory reactionrate to be achieved while minimising the risk of heavies formation.

[0097] Although the use of higher temperatures has heretofore beendisadvantageous because of catalyst deactivation and/or heaviesformation, the process of the present invention, which allows for readyrecycle and reactivation of the catalyst, means that deactivation and/orheavies formation is not disadvantageous and the higher temperatureswill generally enable improved reaction rates. Thus temperatures in therange of from about 95° C. to about 150° C. or higher may be used.

[0098] Thus, for example, in prior art arrangements, an uneconomicsystem is reached where the hydroformylation of the olefin results in aheavies concentration with a recycle stream of greater than 60 wt %within a period of 200 days, through either the use of elevatedtemperatures and/or presence of involatile material in the feed orformed in the reaction system. In contrast, in the present invention,this level of heavies may be accommodated.

[0099] Elevated pressures are also typically used in thehydroformylation zone. Typically the hydroformylation reaction isconducted at a total pressure of from about 4 bar upwards up to about 75bar or more. Usually it will be preferred to operate at a total pressureof not more than about 35 bar.

[0100] In operating the process of the invention in a continuous mannerit is desirable to supply make up amounts of hydrogen and carbonmonoxide in an approximately 1:1 molar ratio, for example about a 1.05:1molar ratio. The formation of such mixtures of hydrogen and carbonmonoxide can be effected by any of the methods known in the art forproducing synthesis gas for hydroformylation, e.g. by partial oxidationof a suitable hydrocarbon feedstock such as natural gas, naptha, fueloil or coal.

[0101] In operating the process of the invention the total pressure ofhydrogen and carbon monoxide in the hydroformylation zone can range fromabout 1.5 bar or less up to about 75 bar or more. The partial pressureof hydrogen may exceed that of carbon monoxide, or vice versa. Forexample the ratio of the partial pressures of hydrogen and of carbonmonoxide may range from about 10:1 to about 1:10. In general, it willusually be desirable to operate at a partial pressure of hydrogen of atleast about 0.05 bar up to about 30 bar and at a partial pressure ofcarbon monoxide of at least about 0.05 bar up to about 30 bar.

[0102] Product recovery can be effected in any convenient manner. Insome instances, for example when using butene-1 or butene-2 as theolefinically unsaturated compound, it is possible to utilise a gasrecycle process similar to that described in GB-A-1582010 which isincorporated herein by reference.

[0103] More usually, however, it will be convenient to withdraw aportion of the liquid reaction medium from the hydroformylation zoneeither continuously or intermittently and to distil this in one or morestages under normal, reduced or elevated pressure, as appropriate, in aseparate distillation zone in order to recover the aldehyde product(s)and other volatile materials in vaporous form;

[0104] the rhodium-containing liquid residue being recycled to thehydroformylation zone either directly or via process steps (f) to (i).

[0105] Condensation of the volatile materials and separation thereof,e.g. by distillation, can be carried out by any conventional means.Aldehyde product(s) can be passed on for further purification, whilst astream containing unreacted olefin can be recycled to thehydroformylation zone together with any hydrogen and carbon monoxidedissolved in the reaction medium. A bleed stream can be taken from therecycle stream or streams in order to control build up of inerts (e.g.N₂) and of hydrogenation product(s) in the recycle streams.

[0106] When using aldehyde condensation products as solvent, the ratioof aldehyde to such products in the liquid reaction mixture in thehydroformylation zone may vary within wide limits. Typically this ratiolies in the range of from about 1:5 to about 5:1 by weight.

[0107] Under appropriate conditions aldehyde productivities in excess ofabout 0.5 g. mole/liter/hr can be achieved in the process of theinvention. Hence it is usually preferred to supply make up olefin to thehydroformylation zone at a rate which corresponds to the aldehydeproductivity of the system under the hydroformylation conditionsselected. As the conversion per pass will usually be less than 100%,typically about 15% to about 80% or higher, it will be necessary toincrease correspondingly the feed rate of the make up olefin if theprocess is to operate on a “once through” basis or to recycle unreactedolefin at an appropriate rate if the process operates with olefinrecycle. Often the aldehyde productivity rate exceeds about 1.0 g.mole/liter/hr, e.g. up to at least about 2 g. moles/liter/hr and therate of supply of make up olefin must then equal or exceed this value.

[0108] At least one stream removed from the reactor will be subjected tothe catalyst recovery steps (e) to (i).

[0109] The reactor stream may be any stream which is obtained from anypoint in the hydroformylation reaction process and which will containmetal hydride catalyst in solution. Thus catalyst may be removed fromthe reactor, in product stream or in other streams including purgestreams. These streams may be treated in accordance with steps (e) to(i) of the present invention to recover the catalyst in a form which issuitable for return to the reactor. The whole of the stream may besubjected to the steps or the stream may be split and a portion thereofsubjected to steps (e) to (i). The remainder of the stream may berecycled to the reactor.

[0110] The reactor stream or a part thereof may be passed directly fortreatment in accordance with steps (e) to (i) or may first undergo anysuitable pretreatment. Where the reactor stream is a product stream, thereaction product may be present during the recovery process of thepresent invention or may be removed at least partially before the streamis contacted with the absorbent.

[0111] The various streams from the reactor, following suitablepre-treatment, such as to remove product may be combined for treatmentthrough a single plant suitable for steps (e) to (i). Alternatively,each stream may be treated separately or streams with similarcompositions may be treated together.

[0112] The fluid stripping medium of step (g) may comprise hydrogen anda process compatible solvent in a single fluid phase, which may be asupercritical phase. In one alternative arrangement the fluid strippingmedium comprises hydrogen and a process compatible solvent in a twophase system. In one arrangement, the process compatible solvent may bea solvent or reactant of the reaction.

[0113] Where the fluid stripping medium comprises a liquid phase and agas phase, the ratio of the gas phase to the liquid phase may be anysuitable value. One suitable example would be one volume of gas to tenvolumes of liquid.

[0114] Where the fluid is a single phase, the ratio of dissolvedhydrogen to solvent present may be any suitable value and may be similarto that used for the two phase system. An important parameter is that anappropriate amount of hydrogen is present.

[0115] In one arrangement, the solvent is a liquid which is contactedwith a gas phase including hydrogen until it is partially or totallysaturated with dissolved gases. The liquid may then be separated fromthe gas phase prior to being passed over the metal containing absorbentas a single phase. The saturated solution may be increased in pressurebefore being passed over the absorbent as the stripping medium.

[0116] Supercritical propane or carbon dioxide may be used as processcompatible solvent. In this arrangement, a supercritical mixtureincluding hydrogen, an optional co-solvent, and ligand may be used asthe stripping fluid.

[0117] In a preferred arrangement of the present invention the acidicabsorbent is an acidic ion exchange resin. The resin may be a styrenedivinylbenzene copolymer containing sulphonic acid groups or carboxylicacid groups. The resin may have a siloxane-containing backbone and anacidic functional group attached to the backbone. The acidic functionalgroup is preferably selected from the group consisting of aromaticcarboxylic acids, aliphatic carboxylic acids, aromatic sulphonic acidsand aliphatic sulphonic acids, with the sulphonic acids beingparticularly preferred.

[0118] Preferably the resin is used in the protonated form. Thus wherethe sulphonic acid groups are the active groups, they are in the form—SO₃H and in the presence of phosphines they are at least partially inthe form —SO₃ ⁽⁻⁾[HPR₃]⁽⁺⁾. Neutralized sulphonic acid resins, in whichsome or all of the protons have been exchanged by a cation may also besuitable but are not preferred.

[0119] Particularly preferred resins include Amberlyst™ 15 andAmberlyst™ DPT-1, with Araberlyst™ DPT-1 being most preferred.Amberlyst™ 15 is available from Rohm and Haas (U.K.) Limited of LennigHouse, 2 Mason's Avenue, Croydon CR9 3NB, England and Arnberlyst™ DPT-1ion exchange resin is available from Kvaerner Process Technology Limitedof The Technology Centre, Princeton Drive, Thornaby, Stockton-on-TeesTS17 6PY, England.

[0120] The absorbent may be pre-treated prior to use. The absorbent maybe washed, for example, with methanol to remove water and may also besieved prior to being contacted with the reactor stream.

[0121] Without wishing to be bound by any theory, it is believed thatthe ion-exchange resin or other suitable absorbent will allow theabsorption of the metal hydride species onto its surface by aprotonation and subsequent elimination of hydrogen by the followingreaction:

HRh(X)_(n)+—SO₃H⇄—SO₃Rh(X)_(n)+H₂

[0122] where each X is a liganding group which may be the same ordifferent and n is an integer of from 2 to 5.

[0123] This hydrogen elimination is a reversible reaction and thus themetal species remains as a labile species and can be desorbed by thehydrogen in the fluid stripping medium.

[0124] Whilst the reactor stream may be contacted with the solidabsorbent by any suitable means, the absorbent is preferably a resin bedin a column through which the reactor stream flows. Once the resin bedhas been loaded with the metal, the stripping medium is then preferablypassed through the resin bed and into the reactor. In one alternativearrangement, the reactor stream may be contacted with the absorbent in astirred vessel. In this arrangement, the contact will be a repeatedbatch process.

[0125] The contact of the reactor stream with the solid acid absorbedresin may be carried out at any suitable temperature. Temperatures offrom 0° C. to about 120° C. may be used with those of from about 20° C.to about 100° C. being preferred. A temperature in the region of fromabout 50° C. to about 95° C. is particularly preferred as the highertemperature will facilitate the removal of the metal from solution andits loading onto the absorbent. The temperatures and pressures willgenerally be selected such that any solids formation such ascrystallisation of ligand or ligand oxide is avoided.

[0126] As the catalyst is absorbed onto the resin, a catalyst depletedsolution will remain and may be removed from the system. The furthertreatment of this solution will depend on the content of the stream.Where the reaction stream treated in accordance with the presentinvention is a stream containing heavies, the catalyst depleted solutionwill preferably be removed. The catalyst depleted solution may be passedthrough a conventional catalyst collection system to trap the inactivecatalytic metal and any trace amounts of the catalyst remaining.

[0127] The stream to be treated may be concentrated before beingcontacted with the acidic absorbent. The concentration will preferablyoccur by removal of volatilisable material. The reactor stream or theconcentrated stream may require dilution with a solvent compatible withthe absorbent before it is contacted with the absorbent. Any suitablesolvent may be used. Normally, the solvent will be miscible with thereactor stream or concentrated stream. Suitable solvents include xyleneand toluene.

[0128] Where the stream to be treated includes inactive catalyst thismay be exposed to the absorbent but may not react therewith and if noreaction occurs will be removed with the non-volatile components.

[0129] However, where the inactive catalyst has been deactivated by theformation of clusters, these may be broken before the stream iscontacted with the absorbent such that they can be absorbed by theabsorbent and treated with the stripping medium. By this means thisinactive catalyst may be regenerated such that it may be returned to thereactor and take part in the reaction.

[0130] Thus according to a preferred aspect of the present invention,the stream is preferably passed through an oxidiser where air is passedthrough the solution to break down the clusters before being broughtinto contact with the absorbent. For a rhodium catalyst havingtriphenylphosphine as a ligand, the air will break down the rhodiumclusters by oxidation of the phosphido bridges.

[0131] The oxidiser may also at least partially oxidise any trivalentphosphorous compounds which may be present to the pentavalent form (i.e.conversion from phosphites to phosphates).

[0132] Where the oxidiser is present, the oxidation step, in addition tobreaking up the clusters, may additionally change the oxidation state ofthe metal in that it will be converted to a simple cationic form. ThusRh²⁺ and Rh³⁺ will be formed.

[0133] Additionally or alternatively, the reaction stream may be treatedin accordance with one or more of the organic reagents described in U.S.Pat. No. 4,929,767 and U.S. Pat. No. 5,237,106 which are incorporatedherein by reference.

[0134] To improve the absorbability of the rhodium onto the absorbent,the process may additionally include, treating the catalyst such that itis in a suitable state for absorption. The catalyst preferably issubjected to hydrocarbonylation where it is treated with anorganophosphorous ligand such as triphenylphosphine, carbon monoxide andhydrogen to reform the catalyst in the form Hrh(CO)(PPh₃)₃.

[0135] Once the rhodium has been loaded onto the absorbent, theabsorbent may be washed to further remove impurities. In addition toremoving impurities by means of their not being absorbed by theabsorbent such that they are removed in the catalyst depleted reactorstream or by the washing described above, the absorbent may also serveto remove some impurities. For example, iron, nickel and/or chromium maybe present. These will generally also be absorbed by the absorbent butwill not be retrieved by the stripping medium of the present invention.Thus the stream recycled to the reactor will be free of theseimpurities.

[0136] Whatever pre-treatments of the stream are carried out, andwhatever washing is carried out, if any, the partial pressure of thegaseous phase of the stripping media, or of the hydrogen component ofthe supercritical phase or the fluid phase, for removing the absorbedmetal may be of any suitable value. Partial pressures of about 200 kPaor higher may be particularly advantageous. The upper limit on thepartial pressure will be dictated by the equipment rating.

[0137] The stripping media fluid preferably additionally includes carbonmonoxide. The presence of carbon monoxide has been found to offerimproved results and is particularly appropriate as the catalyst complexincludes CO as a ligand.

[0138] The fluid of the stripping media preferably includes a liquidphase which comprises liquids which are compatible with the reactants,other compounds and products in the hydroformylation zone, such that theproduct stream containing the rhodium catalyst may be returned to thereactor without further processing. The fluid is preferably alsocompatible with product recovery operations.

[0139] In one embodiment of the present invention, the fluid of thestripping media will comprise liquids which are required to be presentin the hydroformylation zone such as ligands and raw materials. Thus,where the catalyst is HRh(CO)(PPh₃)₃ in one arrangement, the liquidphase will comprise triphenylphosphine. Additionally or alternatively,the liquid phase may comprise olefin and/or triphenylphosphine. Thus, apreferred process of the present invention allows that no additionalsubstances are fed to the hydroformylation zone other than thoserequired for or produced in the hydroformylation reaction.

[0140] In one alternative embodiment, the fluid includes material thatis used in the catalyst recovery process but which is inert to thehydroformylation process. The material is preferably recoverable andrecyclable from the hydroformylation zone to the rhodium recoverysection of the plant. One example of suitable material is toluene whichmay be used as a solvent or diluent in the rhodium recovery process.

[0141] Whilst the reactor stream may be contacted with the solidabsorbent by any suitable means, the absorbent is preferably a resin bedin a column through which the stream collected in step (e) flows. Oncethe resin bed has been loaded with the rhodium, the stripping medium isthen preferably passed through the resin bed and into the reactor.

[0142] The stripping process will preferably simultaneously regeneratethe absorbent bed for further subsequent absorption of rhodium from afresh stream. However, it may be advisable to wash the resin at leastperiodically to remove any impurities, ligand and the like which maybuild up over several passes of the reactor stream.

[0143] The stripping may be carried out at similar temperatures to thoseused for the loading. However, lower temperatures favour the rhodiumbeing desorbed and going into solution. Suitable temperatures includefrom about 20° C. to about 70° C. This is particularly the case wherehigher partial pressures of hydrogen are used.

[0144] To allow for continuous treatment of catalyst from the reactor,the plant may include at least two beds of absorbent operated inparallel. The reactor stream will be passed through a first bed ofabsorbent such that the rhodium is substantially removed from thestream. Once the bed has been loaded, the stream will be switched toflow through the second bed. Whilst the second bed is being similarlyloaded, the stripping medium will be applied to the first bed such thatthe rhodium is desorbed. The procedure will then be reversed such thatthe first bed is being loaded while the second bed is being desorbed.Thus in a preferred arrangement, the process is effectively continuous.

[0145] Thus the present invention provides a process the plant for whichis cost-effective to construct and to operate and which enables thecatalyst to be recovered from reactor streams and returned to thereactor.

[0146] A further advantage of the present invention is that wherereactants, ligands and the like are used for the stripping medium andthese are passed via the absorbent where stripping occurs, to thereactor, not only are no additional substances, or only inertsubstances, introduced into the reactor, there are no costs associatedwith the stripping medium.

[0147] The recovery of the catalyst in accordance with the presentinvention may also enable poisoned and/or inhibited catalyst to bereactivated. Without wishing to be bound by any theory, it is believedthat the metal is attracted to the absorbent and the poison/inhibitor isremoved in the catalyst depleted stream.

[0148] The present invention will now be described, by way of examplewith reference to the accompanying drawings in which:

[0149]FIG. 1 is a schematic diagram embodying the process in accordancewith the present invention;

[0150]FIG. 2 is a schematic diagram embodying steps (e) to (i) of thepresent invention;

[0151]FIG. 3 is a graph of aldehyde, heavies and olefin content againsttime for Comparative Example 1;

[0152]FIG. 4 is a graph of aldehyde, heavies and olefin content againsttime for Example 1;

[0153]FIG. 5 is a graph of aldehyde, heavies and olefin content againsttime for Comparative Example 2;

[0154]FIG. 6 is a graph of aldehyde, heavies and olefin content againsttime for Example 2;

[0155]FIG. 7 is a graph of aldehyde, heavies and olefin content againsttime for Comparative Example 3; and

[0156]FIG. 8 is a graph of aldehyde, heavies and olefin content againsttime for Example 3.

[0157] It will be understood by those skilled in the art that thedrawings are diagrammatic and that further items of equipment such asfeedstock drums, pumps, vacuum pumps, compressors, gas recyclingcompressors, temperature sensors, pressure sensors, pressure reliefvalves, control valves, flow controllers, level controllers, holdingtanks, storage tanks and the like may be required in a commercial plant.Provision of such ancillary equipment forms no part of the presentinvention and is in accordance with conventional chemical engineeringpractice.

[0158] As illustrated in FIG. 1, a liquid comprising olefin is fed tothe apparatus in, line 1 where it is joined by a catalyst solution inline 2. The mixed liquids continue in line 3 to the reactor 4. Thereactor is fitted with an agitator 5 which is capable of inducing thegas from the reactor head space into the liquid and anti liquid vortexbaffles (not shown). The reactor is also equipped with an internalcooling coil 6 arranged such that a controlled flow of a fluid enablesthe reactor to be maintained at the desired temperature. Generally anexternal electrical heater (not shown) is used for the start-up of theequipment.

[0159] The reactor 4 is supplied with a 1:1 molar ratio mixture ofcarbon monoxide and hydrogen in line 7. A trim stream of carbon monoxideand/or hydrogen is supplied in line 8 so that the ratio of the gaspartial pressures in the reactor head space can be adjusted to anydesired value. The gas stream 9 is sparged into the base of the reactor.The unreacted gases pass out of reactor 4 by line 11. This stream passesto demister vessel 12 where any catalyst containing liquid droplets arecollected to return to reactor 4 by line 13.

[0160] The gases continue by line 14 to condenser 15 supplied with acoolant fluid in line 16. The resulting condensate passes via line 17 toproduct recovery and the uncondensed gases pass from the system in line18.

[0161] The liquid leaves the hydroformylation reactor 4 and passes tothe product recovery equipment by line 10. Level control devices (notshown) ensure that a constant liquid inventory is maintained in thereactor.

[0162] The liquid in line 10 comprising of catalyst components,hydroformylation products, unreacted olefin feed, hydrogenated,isomerised and unreacted olefin, as well as aldehyde condensationproducts with some dissolved gases passes into vaporiser 19 suppliedwith a heating fluid in line 20.

[0163] The mixture of liquid and vapour passes via line 21 intovapour/liquid separation vessel 22. Vessel 22 is equipped with dropletagglomeration device 23 which is irrigated by a small stream of productfrom line 58 to wash any ligand and rhodium values back into the base ofvessel 22.

[0164] The vapour leaves by line 24 and the liquid leaves by line 25.The liquid in line 25 which is now free of vapour and which comprisescatalyst is pumped by catalyst recycle pump 26 into line 27. A majorportion of the catalyst solution is recycled in line 28 via line 2 tothe reactor 4. It will generally be mixed with any fresh feed from line1 prior to its addition to reactor 4.

[0165] A minor portion of the stream in line 27 is passed in line 29 tothe rhodium recovery unit. Stream 73 will generally comprise recoveredand make up rhodium, recovered and/or make up triphenylphosphine (orother ligand) as well as solvents and hydroformylation reactionby-products.

[0166] The vaporisation conditions of temperature and pressure areadjusted such that the liquid level in vessel 22 is constant and thissets the total liquid inventory of the reaction system.

[0167] The vapours in line 24 pass to condenser 30 which is suppliedwith coolant in line 31. The cooled mixture then leaves by line 32 andjoins the liquid from line 17 in product vessel 33. The liquid passesfrom vessel 33 via line 34 to distillation column 35. The vapour fromvessel 33 passes through line 36 to compressor 37 and then in line 38 todistillation column 35. The compressor 37 and its associated controlequipment (not shown) determines the pressure in vessels 22 and 33 andhence the product vaporisation temperature in vaporiser 19.

[0168] In column 35, which is illustrated with distillation trays, thealdehyde products are recovered as bottom products in lines 39 and 40.Some aldehyde product recirculates through lines 41, 42 and 45 viareboiler 43 provided with a heating fluid in line 44. The heating fluidprovides the energy supply for the distillation.

[0169] The overhead vapours from column 35 are partially condensed inreflux condenser 46 provided with cooling coil 47.

[0170] The uncondensed vapours pass on in line 48 through-compressor 49,line 50 and condenser 51 with cooling coil 52. This arrangementdetermines the pressure in the distillation system as well as providinga higher pressure in the condenser 51.

[0171] The liquid and gas pass by line 53 to separator 54. The gasesleave the system by line 55. The liquid is partially returned as refluxto the upper part of column 35 by line 56 and the nett make of liquid isrecovered in line 57. This liquid can comprise any volatile solventsadded as part of stream 73 which is added into line 28 as well ascomprising unreacted and isomerised olefin and paraffin or othervolatile components of the olefin feed stream 1. This stream (afteroptional further processing) can for example be used in the rhodiumrecovery and recycle section of the equipment.

[0172] In use, the equipment is brought into operation by flushing alloxygen from the system with nitrogen or argon. Then by filling thereactor 4 and vessel 22 with a liquid such as toluene (or pure aldehydeif available) containing dissolved ligand such as triphenylphosphine anda rhodium catalyst precursor complex (such as rhodium dicarbonylacetylacetonate). A liquid recirculation through the reactor 4, vessel22 and lines 25, 28, 2 & 3 is established by pump 26.

[0173] Olefin feed is supplied at a low rate to the system via line 1and carbon monoxide plus hydrogen by line 7. The reactors are warmedtowards operating temperature and the liquid inventory in the systemmaintained by vaporising liquid in vaporiser 19 as required.

[0174] When the reaction starts, which can be noted on instrumentationas gas uptake, the product aldehyde accumulates in the system and thestart-up solvent preferentially leaves. The distillation equipment iscommissioned and solvent progressively leaves the system.

[0175] Eventually aldehyde starts to accumulate in the base of column35. Pressures and temperatures are adjusted until normal operatingconditions are attained and aldehyde product leaves in line 40. Whenheavies start to accumulate in the catalyst recycle solution which canbe determined by analysis of the composition of line 27, a stream ofmaterial is taken from line 29, treated as described below and recoveredand with make-up material returned in line 73.

[0176] Stream 29 is then passed to the rhodium recovery zone which isillustrated in FIG. 2. This stream 29 will first be passed to anevaporator 74, such as a wiped film evaporator, to separate anyremaining volatile components. Volatile components of the stream will beremoved in line 75 and may be subjected to further treatment includingcondensation and separation. Triphenylphosphine may also be removed inline 75.

[0177] The residue of unvaporized portions which will now be aconcentrated stream is passed in line 76 to oxidiser 77 where air isbubbled through the liquid. The air is introduced in line 78 and ispurged in line 79. The air will serve to break any cluster rhodiummolecules so that this previously inactive rhodium can be absorbed bythe ion exchange resin.

[0178] The stream including the rhodium leaves the oxidiser in line 80and is then pumped, by pump 82, to a hydrocarbonylation zone 81. In thisstirred tank vessel, the catalyst containing stream is mixed withtriphenylphosphine added in line 83 and is contacted with hydrogen andcarbon monoxide which is added in line 84. The triphenylphosphine addedvia line 83 may be recycled triphenylphosphine recovered from line 75.

[0179] The carbonylated catalyst is then removed in line 85 and ispassed into the first absorber column 86′ which is packed withion-exchange resin Amberlyst™ DPT-1. The resin bed will be at atemperature in the region of about 75° C. to aid the rate of absorptionof the rhodium by the ion-exchange resin.

[0180] As the stream passes through the absorbent bed, the rhodium isabsorbed onto the resin and the non-volatile heavies and impurities areremoved in stream 87′ for optional further processing. Due to the valueof the rhodium, the stream may be passed through a conventional rhodiumrecovery system (not shown) to collect any catalyst which may passthrough the resin bed, which may be inactive catalyst, for off-siteregeneration.

[0181] Once column 86′ has been loaded, the stream from vessel 81 willbe directed to column 86″ so that the removal of the rhodium can becarried out as a continuous process. When the resin is loaded in column86″, the catalyst depleted stream is removed in stream 87″.

[0182] The rhodium loaded in column 86′ is then stripped from the resinusing a stripping medium which is passed through the column. Where thestripping medium contains a mixture of organic liquids, these will becombined in mixer 88. The liquid phase is preferably a combination ofprocess compatible solvents and/or olefin added in line 89 andtriphenylphosphine added in line 90.

[0183] The olefin may be fresh olefin which will be passed through theresin bed before being added to the reactor. Alternatively, the olefinmay be recycled olefin, isomerised olefin and paraffin recovered fromstreams removed from the hydroformylation reaction zone.

[0184] Similarly, the process compatible solvents may be fresh solventsor recycled solvents recovered from streams removed from thehydroformylation reaction zone or the downstream product recoverysystems.

[0185] The triphenylphosphine may be fresh triphenylphosphine or it maybe recycled, for example from stream 75 of volatile compounds removedfrom the wiped film evaporator 74.

[0186] This combined liquid phase for the stripping medium is removedfrom the mixer 88 in line 91 where it is combined with hydrogen andcarbon monoxide of the gaseous phase which is added in line 92. Thestripping medium will be passed through column 86′ which is held atambient or higher temperature.

[0187] The resulting stream, which will contain rhodium, hydrogen,carbon monoxide, triphenylphosphine and olefin and/or process compatiblesolvents is then returned to the reactor in line 73.

[0188] The removal of the rhodium allows resin bed 86′ to be used toabsorb further rhodium. Resin bed 86″ can then be stripped by repeatingthe process described above. Thus the process can be operated in acontinuous manner.

[0189] Whilst the present invention has been illustrated with onereactor, vaporiser, etc., it will be understood that where appropriatethe numbers of some or all of these could be increased.

[0190] The invention is illustrated further in the following Examples.

COMPARATIVE EXAMPLE 1

[0191] Hydroformylation is carried out on 1-decene in a hydroformylationplant as described above is run with a rhodium concentration in thereactor of 220 ppm, a triphenylphosphine concentration of 10 wt %,hydrogen and carbon monoxide partial pressures each at 30 psi and at areactor temperature of 110° C. such that non-volatile componentsgradually build up in the recycle loop. No material is taken in line 29for catalyst recycle and the system is run until the shut down criterionof excess heavies in the catalyst recycle solution is reached. Thedesign of the plant apparatus imposes a maximum content of heaviesmaterial in the recycle. For the purposes of these examples, the maximumheavies content is taken to be 60 wt %. When this point is reached, therun must be terminated as operation is no longer feasible.

[0192]FIG. 3 illustrates the performance of the reactor where norecycling of the rhodium is used and illustrates the decline of olefinconversion in the reactors and the build up of heavies. In thiscomparative example the heavies concentration exceeds 60 wt % atapproximately 350 hours.

EXAMPLE 1

[0193] The reactor is again run at 110° C. but a purge equivalent to 0.2wt % of the recycle flow is taken and treated to rhodium recovery asdescribed in FIG. 2 and returned to the reactor.

[0194]FIG. 4 illustrates how the conversion of olefin and overallperformance of the reactor reaches a steady state after approximately1000 hours on-line with the heavies being controlled well below 60 wt %allowing the reactor to be run continuously at these conditions.

COMPARATIVE EXAMPLE 2

[0195] Example 1 is repeated with the reactors running at a temperatureof 110° C. and purge rate of 0.2% of the recycle flow. The reactor isstarted with a rhodium concentration of 500 ppm. The feed also containsa poison such that 1 litre of feed contains sufficient poison to reactwith approximately 1 mg of rhodium. The purge from the recycle stream istreated to recover the rhodium but the poison is not separated from therhodium such that it is recycled to the reactor. As a consequence theheavies reaches a steady state level after 500 hours but the activitydeclines as the rhodium is deactivated. The productivity falls offdramatically at around 2500 hours as illustrated in FIG. 5.

EXAMPLE 2

[0196] Comparative Example 2 is repeated except that the poison in thepurge is not reintroduced with the recovered rhodium. After 1000 hoursthe heavies concentration has reached steady state at approximately 50wt %. The olefin conversion levels out but continues a small decline fora further 5000 hours. After 5000 hours steady state is achieved asillustrated in FIG. 6

COMPARATIVE EXAMPLE 3

[0197] Comparative Example 1 is repeated, however in addition to heaviesforming as a result of aldol condensation reactions, the feed contains0.1 wt % involatile material. As a result the level of heavies in therecycle increases more rapidly than shown in Compatative Example 1. Inthis example the maximum allowable heavies concentration is exceededafter only 200 hours as illustrated in FIG. 7.

EXAMPLE 3

[0198] Example 1 is repeated with a feed containing 0.1 wt % involatilematerial and an increased purge rate of 0.4 wt %. As illustrated in FIG.8 the heavies in the recycle reaches a stable maximum of approximately50 wt % after 1000 hours.

EXAMPLE 4

[0199] A solution of hexene (50 ml) in texanol (50 ml) washydroformylated to extinction using a catalyst prepared from 0.1 mmol ofRhodium(acac)(CO)2 and 0.6 mmol of a bidentate phosphite of the formula(ArO)2P(OAr—ArO)P(OAr)2 where Ar represents various aryl functionalgroups. Amberlyst DPT-1 was then added to the autoclave (8 g, dryweight). After stirring at 65° C. for 1 hour the concentration ofrhodium in solution had dropped to 25 ppm. The autoclave was thenpressurised to 1000 psig with hydrogen and cooled to room temperature.After 18 hours the concentration of rhodium in solution had increased to75 ppm.

1. A continuous hydroformylation process for the production of analdehyde by hydroformylation of an olefin which comprises: (a) providinga hydroformylation zone containing a charge of a liquid reaction mediumhaving dissolved therein a rhodium hydroformylation catalyst comprisingrhodium in combination with carbon monoxide and a ligand; (b) supplyingthe olefin to the hydroformylation zone; (c) maintaining temperature andpressure conditions in the hydroformylation zone conducive tohydroformylation of the olefin; (d) recovering from the liquidhydroformylation medium a hydroformylation product comprising aldehyde;(e) recovering from the hydroformylation zone a stream comprising therhodium catalyst; (f) contacting at least a portion of the stream with asolid acidic absorbent under process conditions which allow at leastsome of the rhodium to become bound to the absorbent; (g) subjecting therhodium bound to the absorbent, under process conditions which allowdesorption of the metal, to a fluid stripping medium comprising hydrogenand solvent; (h) recovering the rhodium hydride catalyst; and (i)recycling the rhodium hydride catalyst to the hydroformylation zone. 2.A process according to claim 1 wherein the stream from step (e) isdivided and a first part is recycled to the hydroformylation zone and asecond part is subjected to steps (f) to (i).
 3. A process according toclaim 2 wherein the second part is at least about 0.01% of the streamfrom step (e).
 4. A process according to any one of claims 1 to 3wherein the olefin is one of more olefin selected from C₂ to C₂₀olefins.
 5. A process according to any one of claims 1 to 4 wherein theolefin is not subjected to pretreatment before being charged to thehydroformylation zone.
 6. A process according to any one of claims 1 to5 wherein the rhodium hydride catalyst is a rhodium carbonyl complexcomprising rhodium in complex combination with triphenylphosphine.
 7. Aprocess according to any one of claims 1 to 6 wherein thehydroformylation zone is operated at a temperature which will causethermal deactivation of the catalyst.
 8. A process according to any oneof claims 1 to 6 wherein the hydroformylation zone is operated at atemperature of from about 40° C. to about 180° C.
 9. A process accordingto any one of claims 1 to 8 wherein the feed to the hydroformylationzone includes poisons, inhibitors or poisons and inhibitors.
 10. Aprocess according to claim 9 wherein the hydroformylation zone includesat least 0.5 gram equivalent of rhodium of poisons, inhibitors orpoisons and inhibitors per cubic meter of feed.
 11. A process accordingto any one of claims 1 to 10 wherein the feed to the hydroformylationzone includes heavies or compounds likely to form heavies in thehydroformylation zone or both.
 12. A process according to any one ofclaims 1 to 11 wherein the fluid stripping medium is a single fluidphase.
 13. A process according to claim 12 wherein the single fluidphase is a supercritical phase.
 14. A process according to claim 12wherein the fluid stripping medium comprises two fluid phases.
 15. Aprocess according to any one of claims 1 to 14 wherein the streamcollected in step (e) contains non-volatile by-products of the reaction.16. A process according to any one of claims 1 to 15 wherein the streamhaving been contacted with the solid acidic absorbent is removed.
 17. Aprocess according to any one of claims 1 to 16 wherein the acidicabsorbent is an ion-exchange resin.
 18. A process according to any oneof claims 1 to 17 wherein the acidic absorbent is a styrene divinylcopolymer containing sulphonic acid groups or carboxylic acid groups.19. A process according to any one of claims 1 to 18 wherein the acidicabsorbent has a silica-containing backbone and an acidic functionalgroup attached to the silica.
 20. A process according to claim 19wherein the acidic functional group is an aromatic carboxylic acid, analiphatic carboxylic acid, an aromatic sulphonic acid or an aliphaticsulphonic acid.
 21. A process according to any one of claims 1 to 20wherein the acidic absorbent is Amberlyst™ 15 or Amberlyst™ DPT-1.
 22. Aprocess according to any one of claims 1 to 21 wherein step (g) iscarried out at a temperature of from about 20° C. to about 100° C.
 23. Aprocess according to claim 22 wherein the temperature is in the regionof about 50° C. to about 95° C.
 24. A process according to any one ofclaims 1 to 23 wherein the stream recovered in step (e) is concentratedprior to contact with the acidic absorbent.
 25. A process according toany one of claims 1 to 24 wherein the stream recovered in step (e) isdiluted with a solvent compatible with the absorbent before it iscontacted with the absorbent.
 26. A process according to any one ofclaims 1 to 25 wherein the stream recovered in step (f) is subjected tooxidation to break clustered catalyst prior to being contacted with theacidic absorbent.
 27. A process according to claim 26 wherein the streamhaving been subjected to oxidation is treated to hydrocarbonylation. 28.A process according to any one of claims 1 to 27 wherein the gaseousphase of the stripping medium additionally includes carbon monoxide.